Which means that on occasion, I have been doing SLDLs and at other times I did SLDLs but who knew?

I prefer SLDL out of those two, just my preference.

Stiff Leg is the only safe one in my book, Straight Leg is unnatural because the hamstring ties under the knee. So if your knee is locked out, you're putting a massive strain on the hamstring tendon where it gets cut off by the knee joint.